You never speak, why?
If there is a reason, come on, try to tell me
Do not withdraw into yourself like that!
You never speak, why?
I envy you a little bit, you know

But then someone corrected me, saying that in this context "perché-is not interogation "why"..its translated as "because..." ..that the person who talks to the other awaits to complete the sentence,its like when someone makes you a question but already knows the answer"
(http://lyricstranslate.com/en/non-parli-mai-you-never-speak.html-0)

So, is it right "why" or "because..."? Probably it is necessary to listen the song to understand the context..or not?

I agree with the one who corrected you.
I'm Italian, and when I read this lines, I think to a non-interrogative form.
You have to think at this sentence like if it was followed by suspension points. In my opinion, you have to use the "because" instead of "why".
But you can wait for other people's opinion too.

Yes, now I believe 100% that the person who corrected me was right! (I had some doubts only because I found some other translations of this song, all with same mistake, as now I can be sure)
Thanks to everyone for helping!

It depends on which way the accent goes, just for your reference. I make this problem all the time in class. If the accent goes like é it means because if it goes è it means why. I'm pretty sure, though I'm not positive, it could go the other way.